Due to the eco-conscious awareness and the impact of the energy crisis, most people are aware of the importance of the energy. At the same time, the power consumption standards of the household appliances are increased in each country. As a result, people are trend to develop low power consumption, high efficiency appliances. The power consumption of the lighting devices are dramatically huge due to the lighting devices are equipped everywhere. The fluorescent lamps and the high-intensity discharge (HID) lamps have an electronic characterize of negative incremental resistance due to their gas-discharge characterize. Thus, ballasts are necessary to stable the current flowing through the lamp.
FIG. 1 illustrates a conventional schematic of duo stage electronic ballast. The full bridge rectifier formed by the diodes D1˜D4 rectifies an AC power source VAC into a DC power. And the front stage active power factor correction circuit which includes an inductor L, a capacitor C, an active switch S and a diode corrects the power factor on the AC power source side. Then, the resonant inverter with series resonant parallel loaded (SRPL) which includes an active switch S1, S2, an inductor LS, and capacitors CS and CP provides the required power of a load (lamp) and generates an output voltage VO. However, the conventional topology of the electronic ballast includes two control circuits and the conventional electronic ballast has one more power consumption. thus, the efficiency of the power conversion of the conventional electronic ballast is low, the cost of the ballast is high, and the size of the ballast is huge. Moreover, the capacitors of the conventional electronic ballast are electrolytic capacitors so as can just meet the capacitance requirement.
FIG. 2 illustrates a conventional schematic of single stage electronic ballast with high power factor. A controllable half bridge rectifier includes an inductor L, diodes D1 and D2, active switches S1 and S2, and a DC-link capacitor C, an AC source VAC is rectified by the half bridge rectifier and the active switches S1 and S2 are controlled to switch so as to achieve the goal of high power factor control. A DC voltage VDC is generated cross the capacitor C. The DC voltage VDC is a DC voltage resource and the switches S1 and S2 series coupled with a resonant inductor LS and a capacitor CS, and the active switch S2, the resonant inductor LS, and the capacitor CS parallel coupled to a capacitor CP to from the resonant inverter with series resonant parallel loaded c(SRPL). An output voltage Vo is generated over the load. This kind of single stage electronic ballast integrates the front stage and the back stage and share two active switch S1 and S2 so as can omit one control circuit and the number of the component can be reduced. In other words, aforementioned electronic ballast has the advantage of low cost. However, this electronic ballast still needs electrolytic capacitors to increase the capacitance.
Comparing to the conventional the conventional inductance ballast, the electronic ballast has the advantages of low noise, no twinkle, and high power factor. However, the capacitors of the electronic ballast have to be implemented as electrolytic capacitors and it will cause the short life time issue. Thus, most of the ballasts are inductance ballasts currently.
The present invention disclosed a high efficiency electronic ballast which can work under the present intensity discharge lamp without any change. It can provide higher efficient, lower power consumption of lighting system, and better lighting quality of lamps. Moreover, the present invention can provide a stable current to load (lamp) for a long time.